What is the definition of orthostatics?

Definition of Orthostatics

Orthostatics refers to a drop in blood pressure upon standing, specifically defined as a decrease in systolic blood pressure of at least 20 mmHg or a decrease in diastolic blood pressure of at least 10 mmHg within 3 minutes of standing from a supine position. 1, 2

Diagnostic Criteria

• The standard definition includes:

  • Decrease in systolic BP ≥20 mmHg
  • Decrease in diastolic BP ≥10 mmHg
  • Occurs within 3 minutes of standing or during head-up tilt at 60 degrees 1, 2

• Alternative diagnostic criteria may include a decrease in systolic BP to <90 mmHg upon standing 3

Types of Orthostatic Hypotension

According to the European Heart Journal guidelines, orthostatic hypotension can be classified into several types 1:

1. Initial OH

   • Occurs within 0-30 seconds of standing
   • Caused by mismatch between cardiac output and systemic vascular resistance
   • Common symptoms: lightheadedness, dizziness, visual disturbances
   • Common in young asthenic subjects, elderly, and with α-blocker use

2. Classical OH (classical autonomic failure)

   • Occurs within 30 seconds to 3 minutes of standing
   • Caused by impaired increase in systemic vascular resistance in autonomic failure
   • Common symptoms: dizziness, pre-syncope, fatigue, weakness, sensory disturbances
   • Common in elderly and with vasoactive drug use

3. Delayed (progressive) OH

   • Occurs within 3-30 minutes of standing
   • Caused by progressive fall in venous return, diminished vasoconstriction capacity
   • Features prolonged prodrome often followed by rapid syncope
   • Common in elderly, autonomic failure, and with medication use

Pathophysiology

When moving from supine to standing position, there is a significant gravitational shift of blood (approximately 500-1000 mL) away from the chest to the venous capacitance system below the diaphragm 1. This shift occurs primarily within the first 10 seconds of standing.

Additionally, prolonged standing causes high capillary transmural pressure in dependent body parts, resulting in filtration of protein-free fluid into interstitial spaces. This can decrease plasma volume by approximately 15-20% (about 700 mL) within 10 minutes 1.

These changes lead to:

• Reduced venous return to the heart
• Decreased cardiac filling pressure
• Reduced stroke volume and cardiac output

In healthy individuals, compensatory mechanisms include:

• Vasoconstriction of resistance and capacitance vessels in splanchnic, musculo-cutaneous, and renal vascular beds
• Increased heart rate
• Activation of skeletal muscle pump and respiratory pump
• Static increase in skeletal muscle tone

When these compensatory mechanisms fail, orthostatic hypotension occurs 1.

Associated Symptoms

Orthostatic hypotension may present with various symptoms due to inadequate organ perfusion 1, 2:

• Dizziness/lightheadedness
• Pre-syncope or syncope
• Weakness and fatigue
• Visual disturbances (blurring, enhanced brightness, tunnel vision)
• Hearing disturbances (impaired hearing, crackles, tinnitus)
• Pain in neck, shoulders (coat hanger syndrome), low back, or precordial area
• Cognitive impairment

Clinical Significance

Orthostatic hypotension is associated with:

• Increased cardiovascular risk
• Higher risk of falls
• Up to 50% increase in relative risk of all-cause mortality 2
• Impaired quality of life

Diagnostic Testing

The diagnosis is confirmed by:

1. Bedside simplified Schellong test:

   • Measure BP and heart rate after 5 minutes in supine position
   • Repeat measurements after 3 minutes of standing 2

2. Head-up tilt table testing:

   • Recommended if patient cannot stand safely
   • Used when clinical suspicion is high despite normal bedside test
   • Tilt angle of at least 60 degrees 1, 2

Monitoring heart rate response during testing helps differentiate between neurogenic and non-neurogenic causes of orthostatic hypotension 2.

By understanding the definition and pathophysiology of orthostatics, clinicians can better diagnose and manage this common condition that significantly impacts morbidity, mortality, and quality of life.